/*
 * Copyright (c) 2010-2014 lijunlin All Rights Reserved.
 * The software source code all copyright belongs to the author, 
 * without permission shall not be any reproduction and transmission.
 */
package org.walkerljl.commons.util;

import java.io.ByteArrayOutputStream;
import java.io.UnsupportedEncodingException;

import org.walkerljl.commons.Constants;

/**
 * URL decoder.
 */
public class URLDecoder {

	/**
	 * Decodes URL elements.
	 */
	public static String decode(String url) {
		return decode(url, Constants.DEFAULT_ENCODING, false);
	}

	/**
	 * Decodes URL elements. This method may be used for all
	 * parts of URL, except for the query parts, since it does
	 * not decode the '+' character.
	 * @see #decodeQuery(String, String)
	 */
	public static String decode(String source, String encoding) {
		return decode(source, encoding, false);
	}

	/**
	 * Decodes query name or value.
	 */
	public static String decodeQuery(String source) {
		return decode(source, Constants.DEFAULT_ENCODING, true);
	}

	/**
	 * Decodes query name or value.
	 */
	public static String decodeQuery(String source, String encoding) {
		return decode(source, encoding, true);
	}

	private static String decode(String source, String encoding, boolean decodePlus) {
		int length = source.length();
		ByteArrayOutputStream bos = new ByteArrayOutputStream(length);

		boolean changed = false;

		for (int i = 0; i < length; i++) {
			int ch = source.charAt(i);
			switch (ch) {
				case '%':
					if ((i + 2) < length) {
						char hex1 = source.charAt(i + 1);
						char hex2 = source.charAt(i + 2);
						int u = Character.digit(hex1, 16);
						int l = Character.digit(hex2, 16);
						if (u == -1 || l == -1) {
							throw new IllegalArgumentException("Invalid sequence: " + source.substring(i));
						}
						bos.write((char) ((u << 4) + l));
						i += 2;
						changed = true;
					} else {
						throw new IllegalArgumentException("Invalid sequence: " + source.substring(i));
					}
					break;

				case '+':
					if (decodePlus) {
						ch = ' ';
						changed = true;
					}

				default:
					bos.write(ch);
			}
		}
		try {
			return changed ? new String(bos.toByteArray(), encoding) : source;
		} catch (UnsupportedEncodingException ignore) {
			return null;
		}
	}

}